Finite Elements Analysis of LED's Solder Joints During Power Thermal Cycling

Abstract

New LED technologies development is allowing the development of better performance glare-free beam modules in automotive lighting. Yet the thermomechanical fatigue and failure behavior of the LED packaging in the lighting module is affecting the reliability of the LED system by failure at the solder joint. Passive thermal cycling is widely used to evaluate solder joint reliability. Simulation tools allow us to predict the reliability of solder joints by knowledge of the fatigue life. However, during active thermal cycling, the effects of self-heating generate thermal gradients between the LED junction and the substrate, which can decrease the lifetime. Reliability in active thermal cycling is validated through subcomponents and components levels to ensure the reliability of the lighting module. In this work, we are presenting a thermomechanical study to predict the solder fatigue behavior under active thermal cycling by simulation of LED PCB packaging. The time dependent temperature field during active power cycling of a LED packaging with turn indicator is analyzed. Thermal transient and stationary simulations are made. Alternative current signal representative of turn indicator (AC) and constant Current (CC) conditions are considered. Based on the temperature evolution through the package and solder the gradient of temperature is used to evaluate the strain in a 1D model through the package by thermal expansion. Then a thermal simulation coupled with thermomechanical model allows determining the most damaging condition. Finally, a comparison between a passive thermal cycle and an active thermal cycle is made to detect the impact of a temperature gradient during active thermal cycling on fatigue life trends.